A second youth has been sentenced to reformative training over the rape of a 13-year-old girl more than three years ago.

Bryan Ong Jing Chong, 18, had admitted to abetting Alson Tan Yu Seng, also 18, in raping the girl at Tan's flat in Bukit Panjang by pinning her arm to the mattress some time in December 2013.

He had pleaded guilty to gaming in public on Aug 31 last year. Two other charges of sexual penetration and attempted rape were considered during his sentencing.

Tan, who was 13 at the time, has been sentenced to reformative training.

A district court heard that the girl had gone to meet the duo's friend, Tan Wei Guang, 19, at a basketball court one night in December 2013. She had befriended him through Facebook and liked him.

After they finished the game, the four, including the girl, proceeded to Alson Tan's flat to rest.

She and Tan Wei Guang slept on the lower bunk, while Ong and Alson Tan rested on a mattress on the floor next to the bed. The trio then went for a smoke outside.

Alson then suggested they could have sex with the victim. He had, on one occasion in 2013, seen alleged gang headman Koh Rong Guang, 24, rape the victim at a staircase of a block near Yew Tee Foodfare foodcourt. Ong and Tan Wei Guang agreed.

After they returned to the room, Ong managed to pull the victim off the bed onto the mattress on a second attempt. Both he and Tan Wei Guang held the struggling victim down by pinning each of her arms to the mattress. Alson then raped her.

The maximum penalty for rape is 20 years' jail and at least 12 strokes of the cane.